1. Field of the Invention
The invention relates to a method of folding sheet-like elements in a folding station of a folding machine, in which the folding station has at least one folding unit and the sheet-like elements are fed to the folding station in a transporting direction with their leading edge in front and with underlapping. The invention also relates to a folding machine for folding sheets of paper, board and the like, in particular for implementing the method according to the invention, having at least a first folding station, with at least one folding unit and an imbricated feeder for feeding sheets with underlapping to the first folding station over an aligning table, in a first transporting direction.
2. Description of the Related Art
The prior art discloses buckle folding machines. The construction of a buckle folding machine having a multiplicity of buckle folding units can be gathered from German Published, Non-Prosecuted Patent Application DE 10 2004 041 471 A1. A respective buckle folding unit thereof includes a buckle plate and three folding rollers disposed in two folding-roller pairs. Knife folding machines are also known. German Published, Non-Prosecuted Patent Application DE 29 40 360 A1 discloses a single knife folding unit for folding printed and pre-folded sheets. Combination folding machines combine buckle folding units and knife folding units. In a first folding station thereof, buckle folding units produce parallel folds and, in a following folding station, knife folding units produce cross folds. German Published, Non-Prosecuted Patent Application DE 10 2006 055 301 A1 discloses combination folding machines having a plurality of buckle folding units and knife folding units disposed thereafter.
In order to increase the output of folding machines, in other words the productivity thereof, the speed at which the sheets run through the folding machine is usually increased. By virtue of the speed being increased, however, a respective sheet undergoes deformation and damage, which results in the quality being significantly impaired.
German Published, Non-Prosecuted Patent Application DE 103 36 757 A1 discloses methods of folding sheets fed with imbricated overlapping. Using those methods is intended to increase the productivity of the folding machines without the speed at which the sheets run through the machine being increased. For that purpose, nips between folding rollers taking in the sheets are increased and/or decreased in sub-phases of a continuous folding operation in dependence on a folding cycle. Such a procedure is disadvantageous since adaptation of the nip requires complicated mechanical mounting of the folding rollers and also high-cost activation of the drives. A further disadvantage is that successive sheets meet in the folding units and are moved at a relative speed in relation to one another. The sheets may be damaged in that case, and that may result in so-called marking. The movement of the two sheets relative to one another may give rise to increased folding tolerances, electrostatic charging and disruptions in the region of a buckle-plate infeed.